Air is needed for the yeast to work fully, yeast 'breaths' oxygen, 'eats' fermentable sgars, 'exhales' carbondioxide, and 'poop' alcohol. I've heard everything from airation stones, to forcing oxygen into the wort. I've had grand luck with holding the syphon tube from pot to carboy 6-9" to mix in air, then rolling the carboy on the ground to mix in air. Mixing air in worts is aok, NEVER LET AIR MIX WITH FINISHED OR FERMENTING BEER, that's where you'll get infected. Using pure oxygen though might actually kill the yeast, since like us we can't breath pure oxygen because it would burn our lungs up. But being a cellular lifeform yeast might be able to consume pure oxygen, but do't quote me.
Good luck,
Malt Vault

I normally aerate my wort (without O-2) while syphoning from the brewpot and it rarely takes more than 24 hrs to start. Meanwhile, I've been told that fermentation after a 30 second shot of 0-2 normally starts within 8 hours. The faster your fermentation starts, the less chance of infection.